Problem summary: (1) Machine freezes completely – ignores hard reset and requires a power off. (2) No response on power on – Gets to first blank screen but no BIOS startup, no beep. (3) After being switched off, from several minutes to several hours, the machine will then boot again, and starts up XP as normal. Then (1) - time varies, but usually within 10 to 20 minutes.

The problem is consistent and repeatable. The other peripherals (disk, DVD drive, display card, wireless LAN card, floppy drive) were as per previous installation before the upgrade.

Have tried (unsuccessfully):

• Power supply - installed a new and more powerful power supply (350W)• Memory test - ran memtest86+ on the new memory – no errors reported• Graphics: Upgraded to the latest Radeon 9000 display driver, removed the graphics drivers and ran with the standard XP drivers, replaced with a known working but older AGP Pro graphics card• Hard disk: Ran chkdsk – no reported problems. Fdisked, reformatted and reinstalled XP several times• Minimal installation: Removed all peripherals except motherboard, memory, CPU and graphics card – still dead on switchon.